We propose to combine developmental genetic and molecular approaches to analyze the roles played during Drosophila development of two late zygotic lethal loci: 1(1) dishevelled (1(1)dsh) and 1(1) hopscotch (1(1)hop). 1(1)dsh and 1(1)hop are late zygotic lethals that exhibit specific maternal effect phenotypes on embryonic segmentation. Dishevelled embryos are missing all parasegmental and segmental boundaries. Mature embryos exhibit a segment polarity phenotype. Hopscotch embryos exhibit defects in two thoracic segments (T2, T3) and abdominal segment 5 is entirely missing. 1(1)hop and 1(1)dsh are clustered on the X- chromosome at position 10B6-8. We propose to further analyze the early (maternal) and late (zygotic) effects on both hopscotch and dishevelled on embryonic development. Additionally, we will identify the DNA region of the 1(1)hop-1(1)dsh gene cluster in order to analyze the spatial and temporal expression of these genes during Drosophila development.